A flywheel energy storage system is so adapted as to store rotational energy produced by rotating a flywheel disk at a high speed, and the rotation of the flywheel disk is urged with an electric motor. For such a flywheel energy storage system, the rotational energy to be stored can be made greater as the flywheel disk becomes heavier and as it is rotated at a higher speed.
In order to allow the flywheel disk having a heavy weight to rotate at a high speed from its stationary state within a short time, a large-size and large-rated electric motor having a great magnitude of a driving torque is required. Such an electric motor, however, is expensive and a place where it is to be installed should be large, whereby the total system also becomes too large in size.
On the other hand, when the attempt is made to rotate a flywheel disk having a heavy weight at a high speed by an electric motor small in size and to drive the rotation of such a heavy flywheel disk directly by means of an output of the such small-size electric motor, there is the risk that the electric motor becomes in an overload state and it is burned out. Hence, the flywheel disk is required to be rotated gradually by means of a certain transmission mechanism in order to cause no or little overload to be imposed upon the electric motor. This system, however, requires a long time for rotating the flywheel disk at a high speed. Further, such a transmission mechanism produces energy such as heat, resulting in a loss of energy.
The present invention has been performed with the above situation taken into account and the object of the present invention is to provide a device for rotation and a method therefor, capable of efficiently converting sequentially input rotative driving power into the rotational energy of the whole of the layered rotating body of a layer structure. This arrangement allows even a small-sized electric motor to rotate the heavy flywheel disk at a high speed within a short time.